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Date: Wed, 16 Nov 2016 16:20:03 -0500 From: Chris Metcalf <cmetcalf@...lanox.com> To: John Stultz <john.stultz@...aro.org>, Thomas Gleixner <tglx@...utronix.de>, Laurent Vivier <lvivier@...hat.com>, David Gibson <david@...son.dropbear.id.au>, "Christopher S . Hall" <christopher.s.hall@...el.com>, linux-kernel@...r.kernel.org Cc: Chris Metcalf <cmetcalf@...lanox.com> Subject: [PATCH v2] time: Avoid signed overflow in timekeeping_delta_to_ns() This bug was originally fixed in commit 35a4933a8959 ("time: Avoid signed overflow in timekeeping_get_ns()"). When the code was refactored in commit 6bd58f09e1d8 ("time: Add cycles to nanoseconds translation") the signed overflow fix was lost. Re-introduce it in a less subtle way by changing the type of "nsec" to unsigned and adding a comment explaining why. Signed-off-by: Chris Metcalf <cmetcalf@...lanox.com> --- v2: just use "u64 nsec" to fix the signed shift problem kernel/time/timekeeping.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 37dec7e3db43..8c06a2aa9b5f 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -302,7 +302,7 @@ static inline u32 arch_gettimeoffset(void) { return 0; } static inline s64 timekeeping_delta_to_ns(struct tk_read_base *tkr, cycle_t delta) { - s64 nsec; + u64 nsec; /* Avoid possibility of a negative right shift. */ nsec = delta * tkr->mult + tkr->xtime_nsec; nsec >>= tkr->shift; -- 2.7.2
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